The present invention is related to well point systems and especially to the automatic regulation of the flow of water in a well point system.
It is necessary to de-water a construction area when construction work is being done below the surface of the earth in order to remove all water and other liquids from an excavation area to provide dry working conditions. The most common technique of de-watering an excavation area is to sink a plurality of well points around the area and connect a pump to each of the well points so that the water will be pumped from the area surrounding the excavation. This de-watering method has proven quite satisfactory but presents certain problems. As the well points lower the water table or level, the upper portion of the well points tend to draw air through the system which seriously affects the operation of the pumps. This problem is reduced to some degree by elaborate valving devices and large vacuum pumps, but the present practice still requires a manual closing of tuning valves on a well point header system. This is an especially troublesome problem where the different well points are sunk to different depths surrounding the excavation. In a typical condition with a series of well points evenly spaced and evenly located at the same depths, some of them will have evacuated their immediate area of water while an adjacent well point may not have completely evacuated the water depending upon the soil structure and the liquid yield of the soil. The well points drawing air must be isolated from the header manifolds so that a pumping machine is not allowed to draw air. When such points are isolated it is also important to know when and if the water level rises so that they can be returned to the system. Since each point cannot be constantly monitored, a means for eliminating free air entry from a centrifugal pump had to be devised and a vacuum pump was implemented as an essential part of the rig. Even so, without the practice of manual tuning, the air handling capacity of a well point pump is frequently overcome. In order to overcome these problems, several automatic tuning systems for well point systems have been devised including U.S. Pat. No. 3,815,626 for an apparatus for the automatic regulation of the flow of fluid in which the well point has incorporated therein automatic regulation of the flow of water which operates on a rising and falling float in response to the water levels surrounding the well point. In addition, four U.S. Pat. to T. F. Moore, Nos. 2,176,540; 2,164,253; 2,474,364 and 3,888,605 are directed towards well point systems and to the improvement of well point systems by the use of automatic tuning well points and valves. The first three of these patents teach well point systems which work on floats located in the well point responsive to the level of ground water which actuates the float to block the flow of air when the water level drops below a predetermined level. These prior art automatic tuning well points are, however, located in the well point themselves which then must be drilled deep into the earth, thereby substantially increasing the cost of an individual well point which frequently must be left in the earth and increasing the size and complexity of the well point. By increasing the complexity of the well point located deep in the earth a likelihood of failure of the well point is also increased. It is accordingly one advantage of the present invention that an automatic tuning valve for well points may be located above the earth in the riser between the well point and the manifold to shut off a particular riser and well point when the well point starts drawing air.
The fourth U.S. Pat. No. 3,888,605, deals with a float actuated valve located above the surface of the earth for shutting off individual risers of a well point system. However, in this valve a float is located in the flow of water so that the flow of water from the riser tends to pull the float towards its cutoff position during normal operation thereby interferring with the flow of water through the valve while air passageway by-passes the valve to provide a reduced pressure condition in the pipe when the valve means is closed.
One prior U.S. Pat. No. 3,654,434 teaches an apparatus for drying excavations by providing a float actuated valve for bleeding air in a well point system by locating a valve at the highest point and bleeding air from the manifold of the well point system.
One reason that automatic tuning valves have been located in well points rather than above the earth is because the water level is needed to actuate the flow to shut off the air and more importantly, the water level is needed to re-actuate the flow to turn the well point back on when the water level rises.